A generalized diffusion–dissolution model for drug release from rigid polymer membrane matrices

A generalized diffusion–dissolution model for the release kinetics of non-swelling and nondegradable rigid polymer matrices has been proposed by constructing finite dissolution rates for both the dissolved amorphous drug and the dispersed drug particles, respectively. The dissolved amorphous drug in the matrices was visualized as a step-function-type dissolution source releasing drug into the surrounding liquid phase according to the Noyes–Whitney equation. Source layers were applied to describe the dissolution rate for dispersed drug particles, and the focus was played on spherical drug particles with a delta-type dissolution rate based on the Noyes–Whitney equation. Asymptotic cases to the earlier published models have been developed and numerically evaluated to demonstrate the validity and generality of the proposed model. A technique with the Greenʹs function was applied to transform the coupled partial differential equations (PDEs) into implicit integral solutions facilitating the numerical calculations to handle arbitrarily specified model parameters of the PDEs. Further, the integral form solutions provided a better insight into the effects of the meaningful variables on the release behavior than the direct numerical solutions to the PDEs. The effects of the Peclet numbers PeB (the external mass transfer resistance), Peds (the amorphous drug dissolution rate) and Pedp (the dispersed drug particle dissolution rate), have been investigated as well as the effects of the drug solubility in the release medium, the number of source layers, the membrane thickness and/or the particle sizes. It was found that Peds and Pedp have more profound effects on the release behavior, and the significance of other parameters are determined by the conditions of specified Peclet numbers.